docs: def column_rename(self, existing_name, hsh=None):
          """
          Like unique_name, but in addition must be unique to each column of this
          feature. accomplishes this by prepending readable string to existing
          column name and replacing unique hash at end of column name.
          """
          try:
              existing_name = str(existing_name)
          except UnicodeEncodeError:
              pass
          if hsh is None:
              hsh = self._hash()
          if self._name:
              return '%s(%s) [%s]' %(self._name, self._remove_hashes(existing_name),
                      hsh)
          return '%s [%s]'%(self._remove_hashes(existing_name),
                      hsh)